MachineCalcs

K-Factor for Copper Sheet Metal

Copper has no single fixed K-factor, but air-bent ductile coppers commonly start in the K = 0.30-0.40 band, with harder tempers and gentler radius-to-thickness pushing toward 0.45-0.50. The production value is the one you back-solve from a coupon, then compare with the copper starter band on the calculator.

Back-solve copper K-factor K-factor calculator page
k factor for copper copper k factor copper sheet metal k factor

Starting band

Air bending often starts near K = 0.30-0.40 for ductile sheet metals, and soft copper sits comfortably in that band. Harder tempers, larger R/t and bottoming push K upward toward the 0.45-0.50 end; coining shifts it further still.

Why copper needs its own check

Copper and copper alloys can bend differently by temper. Annealed copper, half-hard copper, brass and bronze can move the neutral axis differently under the same tooling.

Coupon workflow

  1. Cut a copper strip with a known flat length.
  2. Bend it with the production punch, die, grain direction and bend angle.
  3. Measure outside legs and inside radius.
  4. Back-solve K with the flat-sample method.
  5. Compare the measured value with the selected copper starter band, then use the coupon result for production flats.

Formula used

The equation does not change for copper. What changes is the measured bend allowance that comes from copper temper and tooling.

K = (BA / theta - R) / t

Frequently asked questions

What K-factor should I use for copper?

Start in the K = 0.30-0.40 air-bending band for soft ductile copper (toward 0.45-0.50 for harder tempers or gentler radii), then replace it with a coupon-measured value before cutting production flats.

Is copper K-factor the same as brass?

No. Copper and brass can be close in some setups, but the alloy and temper should be measured separately for production flats.

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